gemini21, try looking through the yellow pages in your area and finding a bra shop or lingerie boutique. Some of them carry swimsuits even if they don't advertise it. Look for shops that cater to a wide range of sizes they seem to be more likely to carry swimsuits for the, er, above average.

Alternatively, some cities have swimsuit-only shops, I don't know what they are like.

If you are ok with mail-order, you can also try bravissimo.com.

If there is no typo in your post, you might want to get properly fitted at a bra shop. I find it hard to believe that a 34-band size could fit into a 4. It may be that your band size is too big.